This is from my Sewing for the Apparel Industry book. I'm cleaning my scanned folder. The Straight Hemming Stitch is similar to a Fell Stitch--sometimes call an Applique Stitch. For a hem, pick up a single thread on the garment so it doesn't show on the right side; then with the needle on an angle, insert it into the folded edge. For the fell stitch, imagine that the hem is an applique or a patch. The stitches at the edges are perpendicular to the folded edge and the needle is slanted underneath. When properly made, you can't see the thread on the right side. The fell stitch is a favorite of tailors. It's much more secure than the slipstitch. If you are making a small patch on a dress, this is a great stitch.